"Supernatural" showrunner Sera Gamble will step down at the end of the current season, Zap2it has confirmed. After seven years on "Supernatural," Gamble has chosen to focus on developing other material. She has led the show for two seasons, since creator Eric Kripke's role was reduced after Season 5. She'll be replaced by Jeremy Carver, who will work alongside co-showrunner Robert Singer. Carver served as executive story editor and then co-producer of "Supernatural" from Season 3 to Season 5, after which he moved on to the role of executive producer on SyFy's US remake of the UK series "Being Human." He returns to "Supernatural" as showrunner and executive producer, but he will continue to EP "Being Human" as well.Though the network has yet to officially announce a pickup for "Supernatural's" Season 8, fans shouldn't be concerned about cancellation. With stars Jared Padalecki and Jensen Ackles locked in for another season, the CW is unlikely to...